1. Field of the Invention
The present invention relates to a process for producing vacuum deposition films composed of an alloy or an intermetallic compound composed of two or more components having different vapor pressures and to a process for producing vacuum deposition films with good reproducibility regardless of the evaporation time and without variations in the composition of the vacuum deposition film. Particularly, it relates to a process for producing vacuum deposition films which comprises continuously forming a vacuum deposition film composed of an alloy or a compound having a definite composition on an indefinite length base or sheet.
2. Description of the Prior Art
When vacuum evaporation is carried out using an alloy or an intermetallic compound of components having different vapor pressures by means of a single evaporation source, the composition of the vacuum deposition film is generally very different from the composition of the evaporating material because of the difference in the vapor pressure and the evaporation rate of each component.
Combinations of metals, namely, alloys in which the composition of the resulting vacuum deposition film is substantially the same as that of the evaporating material, have been described in Vacuum Deposition of Thin Films, by Holland, Chapman and Hall Ltd. (1963), page 188. However, they are quite exceptional and are very unique combinations.
Hitherto, though various processes have been proposed for producing the vacuum deposition films of an alloy or an intermetallic compound of two components having different vapor pressures, they all have faults on practical use.
For example, there is the so-called simultaneous vacuum evaporation process which comprises evaporating each component by means of respective evaporation sources and producing a vacuum deposition film having the desired composition by controlling the evaporation rate of each component. However, there are many difficulties such as in controlling the evaporation rate of elements from each evaporation source, the geometric arrangement of each evaporation source or of the evaporation source and the base, or radiant heat from each evaporation source applied to the base, etc. Thus, in order to produce the vacuum deposition films of the alloy or the intermetallic compound having a composition within a definite range, it is necessary to control the evaporation rate of each component. For this purpose, a precise control apparatus is necessary. Particularly, in case of continuous vacuum evaporation, this control is very difficult to carry out, because the volume of the evaporation sources is large. Further, in the case of continuous vacuum evaporation the volume to be evacuated is large due to the large volume required by two evaporation sources therein, by which it becomes necessary to provide a large scale evacuation apparatus having a high evacuation ability and thus costs for equipment, operation and maintenance cannot be disregarded.
A process for producing the vacuum deposition films of the alloy or the intermetallic compound using a single evaporation source has been proposed. It comprises continuously dropping a powdery evaporating material composed of the alloy or the compound in a suitable amount into the evaporation source and instantaneously evaporating the powdery evaporating material to produce the vacuum deposition film. According to that process, though it is supposed that a vacuum deposition film having the same composition as that of the evaporating material can always be obtained without regard to the vacuum evaporation time, there are the following problems. Namely, it is very difficult to uniformly drop the powdery evaporating material in a definite amount and the thickness of the films often varies according to the dropping condition. Further, it is difficult to produce an alloy powder having a suitable composition as the evaporating material, and it is often impossible to obtain an alloy powder having the desired composition. Even if a powdery mixture of simple metal substances is used, not only much labor is necessary for uniformly blending but also the mixture becomes nonuniform upon dropping into the evaporation source due to difference in the particle size and specific gravity of the metals in the mixture, and it is consequently difficult to produce the vacuum deposition films having a uniform composition. Further, since the metal powder is rapidly exposed to high temperature upon dropping into the evaporation source it scatters around and cannot be effectively used as the evaporating material. The scattered material adheres to the vacuum deposition film and, consequently, good vacuum deposition films often cannot be obtained.
Further, a process has been proposed which comprises continuously feeding a two component alloy wire having a desired composition to a single evaporation source and instantaneously evaporating the fed alloy wire to produce a vacuum deposition film having the same composition as that of the evaporating material. However, it is often difficult to obtain an alloy wire having a composition suitable for producing vacuum deposition films having a given composition. Further, the vacuum deposition films having a different composition by the evaporation time are often formed, because the composition of the vacuum deposition film gradually varies by the difference of vapor pressure, namely, the difference of evaporation rate, of each component composing the alloy wire.